Non-violently resisting arrest is a real thing and should most certainly be a crime. E.g. you put your hands firmly across your chest and force the police to overpower you and force you into handcuffs. You're not attacking anyone, but you're resisting arrest in a way that threatens the safety of the arresting officers and obstructs the lawful execution of an arrest warrant.

Also, when the charges are all for the same crime, the sentences are almost always concurrent, which means they run at the same time. It doesn't actually increase the length of the prison sentence.